1. Field of the Invention
The present invention relates to the field of integrated circuit devices, and in particular to electrical contact pads formed on silicon substrates employing aluminum metalization.
2. Description of the Prior Art
Alloy pitting is a well known phenomena in the integrated circuit arts. When aluminum is alloyed to silicon, within the temperature range of 400.degree. to 500.degree. C., silicon is drawn into the aluminum layer by virtue of the high solid solubility of silicon in aluminum. The prior art has devised various elaborate and esoteric methodologies and structures to deal with this phenomenon in aluminum-silicon contact pads. For example, the prior art has devised or employed silicon doped aluminum, platinum-silicide layers, multilayer metallic contacts, silicon gettering layers and so forth.
As a result of the high solubility of silicon in aluminum, unless some offsetting measure is adopted, the aluminum would migrate into the underlying diffusion layer penetrating the junction depletion region and thereby interfering with the efficient operation of the semiconductor device by increasing reverse leakage current. In the extreme case, the aluminum may punch through a shallow diffusion region thereby completely shorting out the diffusion region.
What is needed is a simplified aluminum-silicon contact which may be fabricated without complicated or costly methodologies and which will be characterized by the substantial elimination of alloy pitting, even in shallow diffusion regions.